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C++ Program For Deleting Last Occurrence Of An Item From Linked List

  • Last Updated : 28 Mar, 2022

Using pointers, loop through the whole list and keep track of the node prior to the node containing the last occurrence key using a special pointer. After this just store the next of next of the special pointer, into to next of special pointer to remove the required node from the linked list.

C++




// C++ program to implement the
// above approach
#include <iostream>
#include <bits/stdc++.h>
using namespace std;
 
// A linked list Node
struct Node
{
    int data;
    struct Node* next;
};
 
// Function to delete the last
// occurrence
void deleteLast(struct Node** head,
                int x)
{
    struct Node** tmp1 = NULL;
    while (*head)
    {
        if ((*head)->data == x)
        {
            tmp1 = head;
        }
        head = &(*head)->next;
    }
    if (tmp1)
    {
        struct Node* tmp = *tmp1;
        *tmp1 = tmp->next;
        free(tmp);
    }
}
 
// Utility function to create a new
// node with given key
struct Node* newNode(int x)
{
    Node* node = new Node ;
    node->data = x;
    node->next = NULL;
    return node;
}
 
// This function prints contents of
// linked list starting from the given
// Node
void display(struct Node* head)
{
    struct Node* temp = head;
    if (head == NULL)
    {
        cout << "NULL";
        return;
    }
    while (temp != NULL)
    {
        cout << temp->data <<
                " --> ";
        temp = temp->next;
    }
    cout << "NULL";
}
 
// Driver code
int main()
{
    struct Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next =
    newNode(4);
    head->next->next->next->next =
    newNode(5);
    head->next->next->next->next->next =
    newNode(4);
    head->next->next->next->next->next->next =
    newNode(4);
     
    cout << "Created Linked list: ";
    display(head);
     
    // Pass the address of the head
    // pointer
    deleteLast(&head, 4);  
    cout << "List after deletion of 4: ";
     
    display(head);   
    return 0;
}
// This code is contributed by khushboogoyal499

Output:

Created Linked list: 1 --> 2 --> 3 --> 4 --> 5 --> 4 --> 4 --> NULL
List after deletion of 4: 1 --> 2 --> 3 --> 4 --> 5 --> 4 --> NULL

Given a linked list and a key to be deleted. Delete last occurrence of key from linked. The list may have duplicates.

Examples:  

Input:   1->2->3->5->2->10, key = 2
Output:  1->2->3->5->10

The idea is to traverse the linked list from beginning to end. While traversing, keep track of last occurrence key. After traversing the complete list, delete the last occurrence by copying data of next node and deleting the next node.  

C++




// A C++ program to demonstrate deletion
// of last Node in singly linked list
#include <bits/stdc++.h>
 
// A linked list Node
struct Node
{
    int key;
    struct Node* next;
};
 
void deleteLast(Node* head,
                int key)
{
    // Initialize previous of Node
    // to be deleted
    Node* x = NULL;
 
    // Start from head and find the
    // Node to be deleted
    Node* temp = head;
    while (temp)
    {
        // If we found the key,
        // update xv
        if (temp->key == key)
            x = temp;
 
        temp = temp->next;
    }
 
    // Key occurs at-least once
    if (x != NULL)
    {
        // Copy key of next Node to x
        x->key = x->next->key;
 
        // Store and unlink next
        temp = x->next;
        x->next = x->next->next;
 
        // Free memory for next
        delete temp;
    }
}
 
/* Utility function to create a
   new node with given key */
Node* newNode(int key)
{
    Node* temp = new Node;
    temp->key = key;
    temp->next = NULL;
    return temp;
}
 
// This function prints contents of
// linked list starting from the
// given Node
void printList(struct Node* node)
{
    while (node != NULL)
    {
        printf(" %d ",
               node->key);
        node = node->next;
    }
}
 
// Driver code
int main()
{
    // Start with the empty list
    struct Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next =
    newNode(5);
    head->next->next->next->next =
    newNode(2);
    head->next->next->next->next->next =
    newNode(10);
 
    puts(
    "Created Linked List: ");
    printList(head);
    deleteLast(head, 2);
    puts(
    "Linked List after Deletion of 1: ");
    printList(head);
    return 0;
}

Output: 

Created Linked List: 
1  2  3  5  2  10 
Linked List after Deletion of 1: 
1  2  3  5  10

The above solution doesn’t work when the node to be deleted is the last node.
Following solution handles all cases. 

C++




// A C++ program to demonstrate deletion
// of last Node in singly linked list
#include <bits/stdc++.h>
using namespace std;
 
// A linked list Node
struct Node
{
    int data;
    struct Node* next;
};
 
// Function to delete the last
// occurrence
void deleteLast(struct Node* head,
                int x)
{
    struct Node *temp = head,
                *ptr = NULL;
    while (temp)
    {
        // If found key, update
        if (temp->data == x)
            ptr = temp;       
        temp = temp->next;
    }
 
    // If the last occurrence is the
    // last node
    if (ptr != NULL &&
        ptr->next == NULL)
    {
        temp = head;
        while (temp->next != ptr)
            temp = temp->next;      
        temp->next = NULL;
    }
 
    // If it is not the last node
    if (ptr != NULL &&
        ptr->next != NULL)
    {
        ptr->data = ptr->next->data;
        temp = ptr->next;
        ptr->next = ptr->next->next;
        free(temp);
    }
}
 
/* Utility function to create a new
   node with given key */
struct Node* newNode(int x)
{
    Node* node = new Node ;
    node->data = x;
    node->next = NULL;
    return node;
}
  
// This function prints contents of
// linked list starting from the given
// Node
void display(struct Node* head)
{
    struct Node* temp = head;
    if (head == NULL)
    {
        cout << "NULL";
        return;
    }
    while (temp != NULL)
    {
        cout <<" --> "<< temp->data;
        temp = temp->next;
    }
    cout << "NULL";
}
 
// Driver code
int main()
{
    struct Node* head = newNode(1);
    head->next = newNode(2);
    head->next->next = newNode(3);
    head->next->next->next =
    newNode(4);
    head->next->next->next->next =
    newNode(5);
    head->next->next->next->next->next =
    newNode(4);
    head->next->next->next->next->next->next =
    newNode(4);
    cout <<
    "Created Linked list: ";
    display(head);
    deleteLast(head, 4);
    cout <<
    "List after deletion of 4: ";
    display(head);
    return 0;
}
// This code is contributed by shivanisinghss2110

Output: 

Created Linked List: 
1  2  3  4  5  4  4 
Linked List after Deletion of 1: 
1  2  3  4  5  4

Please refer complete article on Delete last occurrence of an item from linked list for more details!


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